test: fix flaky test-benchmark-fs

Some benchmarks may return 0 operations with the new very short duration
provided by the test program. Set environment variable to allow that.

PR-URL: #17885
Reviewed-By: Anna Henningsen <[email protected]>
Reviewed-By: Colin Ihrig <[email protected]>
Reviewed-By: James M Snell <[email protected]>
Reviewed-By: Weijia Wang <[email protected]>

Author: Trott

test/parallel/test-benchmark-fs.js

@@ -16,4 +16,4 @@ runBenchmark('fs', [
   'statSyncType=fstatSync',
   'encodingType=buf',
   'filesize=1024'
-], { NODE_TMPDIR: common.tmpDir });
+], { NODE_TMPDIR: common.tmpDir, NODEJS_BENCHMARK_ZERO_ALLOWED: 1 });